Bistable stereoscopic 3D percepts: Will-power, flip frequency, eye movements and blinks

Abstract

Conscious perception can be influenced by the observer's intention. Insights in conscious perception stem mainly from binocular rivalry studies in which the alternative percepts flip without clear voluntary control. We studied voluntary control in perception by exposing the visual system to a novel ambiguous 3D stimulus. In our paradigm observers estimate the orientation of a grid in 3D space (a metrical task). Perspective- and disparity-specified grid orientations can be independently varied across stimulus presentations, enabling us to do quantitative signal processing analysis. We have previously reported that observers are able to attentively select either a perspective- or a disparity-dominated percept when the two specified orientations had opposite signs (van Ee et al., Journal of Vision, 2002, 2, 597–607). Here we measured (i) the duration that an observer is able to voluntarily keep one percept over the alternative percept and (ii) the normal percept-dominance duration when the observer does not try to keep one over the other percept. We examined the increase in percept-dominance duration due to voluntary control, for both our stimuli and the classical binocular rivalry stimuli (horizontal/vertical bars and the house/face). Although spontaneous flips could not be prevented, we found a clear increase in percept-dominance duration for our stimulus relative to the classical stimuli. For a number of subjects the increase was almost ten-fold. We also measured eye movements and found that perceptual flips were neither correlated with eye movements, nor with blinks. Thus, will-power seems to have a relatively large influence in our bistable stimulus providing conditions for well-controlled conscious perception experiments.